PID calculations for the _pid structure *a. This function uses the positional form of the pid equation, and incorporates an integral windup prevention algorithim. Rectangular integration is used, so this function must be repeated on a consistent time

TI提供的VLIB库函数应用，这个是个积分函数，可以在DM6437开发板上运行-the function is VLIB function libary by TI programmed,and can running on the DM6437 platform